Outlook sync, send/receive schedule best practices

Has anyone tested the sync performance with the normal send/receive schedule set to occur every x number of minutes vs. no schedule? I am having problems with multiple users where mail will come into their zimbra inbox but will take a long time to sync with outlook (2003), up to 30 mins. We have about 50 users connecting to a hosted zimbra server on a 7mbps synchronous internet connection (wireless WAN).

There seems to be a lack of solid info out there about the syncing and send/receive that outlook performs when connected to zimbra via the ZCO. I know that Zimbra syncs with outlook via MAPI and I have found that when the ZCO is installed and it creates a new profile, the profile send/receive schedule is NOT set automatically perform a send/receive on a set schedule. I am assuming that the type of sync that outlook performs with zimbra does not require a scheduled send/receive but I cannot find info anywhere to confirm this.

We use GetOutgoingQueues. We sync once a minute, or if you hit the Send/Receive button. All syncs go both ways except the initial sync from the server to Outlook when you create an Outlook profile. If messages are sitting on the Zimbra server for 30 minutes before you see them in Outlook, then there is a problem. Sometimes with Outlook 2003, it didn't really shut down correctly (those problems have been corrected in 2007), and syncs are not really working. After exiting Outlook 2003, make sure that Outlook 2003 is really shut down (use the Task Manager).

If you are having problems, and can duplicate where messages sit on the Zimbra server for a half an hour, enable ZCO logging, and send the logs.